1. Field of the Invention
The present invention is directed to a positioning arrangement of the type having a seating surface for an examination subject to be examined in a computed tomography apparatus, and which has a recess into which a reference member can be introduced.
2. Description of the Prior Art
Such positioning arrangements are employed for the implementation of osteo-examinations wherein the aim is to determine the density values of the bone material of a patient on the basis of a reference member formed of a defined material. For these examinations, the reference member must assume a defined position relative to the patient; namely, it must be positioned relative to the longitudinal axis of the patient so that it produces an image in the examination of a diagnostically relevant region of the patient. Second, it must exhibit a defined spacing from the body surface of the patient.
In this context, U.S. Pat. No. 4,233,507 discloses that reference members be fixed in a positioning plate serving for the positioning of the patient. It is difficult if not impossible to replace reference members in this case. This publication also discloses that reference members be arranged in a removable part of the positioning plate.
U.S. Pat. No. 4,651,335 discloses the use of a positioning pillow or cushion containing reference members, these being arranged between the patient and a positioning plate serving for the positioning of the patient. It is difficult to assure an exact positioning of the reference members relative to the patient in this case.
U. S. Pat. No. 4,870,666 discloses a positioning means of the type initially described that is fashioned as a cushion that can be placed on a positioning plate, the upper side of the positioning plate being provided with a recess for the acceptance of reference members.
A positioning mat that can be placed on a positioning plate is also known that has a receptacle that is covered with a glued-on foil at the underside of the positioning plate. The reference members are placed into this receptacle proceeding from above, i.e. proceeding from the seating surface of the positioning mat.
Additional cushions or spacers of expanded cellular material are required with this positioning mat in order to be able to correctly position the reference member relative to the patient; one cushion maintains the correct position of the reference member in the direction of the longitudinal axis of the patient, and another cushion assures the correct spacing of the reference member from the body surface of the patient.
This known arrangement also has a number of serious disadvantages. The clearance for the reference member is open toward the patient, so that body fluids can penetrate, these being difficult to remove. In particular, the corners cannot be disinfected in a satisfactory manner. The reference body, which is freely exposed at the top, presses against the patient""s back. Additional cushions of expanded cellular material are required in order to position the reference member in the correct position relative to the patient, these being easily lost in routine clinical work. During storage, the reference member easily falls out of the positioning mat. Lastly, the glued location between positioning mat and foil frequently tears.
An object of the present invention is to provide a positioning arrangement of the type initially described which can be dependably handled.
This object is inventively achieved in a positioning arrangement having a positioning element seating surface for an examination subject to be examined in a computed tomography procedure, this positioning procedure being provided with a recess at its underside into which a reference member can be introduced.
The seating surface can be smooth since, in the inventive positioning arrangement, the recess (preferably adapted in shape to the reference member) is provided at the underside of the positioning means facing away from the seating surface. Differing from known positioners, no contaminants can collect in the mounting region for the reference member. Contaminants can be easily removed and it is easy to disinfect the seating surface.
In a preferred embodiment of the invention, the recess has a holder for the reference body that places the reference body introduced into the recess into a defined position relative to the seating surface. The correct position of the reference body relative to the seating surface, and thus relative to the patient is assured by the recess being adapted in shape to the reference member and being provided with this holder, without requiring additional cushions of expanded cellular material for the correct positioning of the reference member.
In one version of the invention, the reference member is held with a positive fit in the recess, so that the reference member can remain in the recess when the positioning arrangement is in storage. It is thus assured that the reference is always present when the positioning arrangement is employed and cannot be lost.
In an embodiment of the press fit, the reference member can be introduced into the recess with plastic deformation of the positioning element, so that it can in turn be removed asa needed, for example in order to replace it with a different reference member.
All materials that exhibit an adequately low X-ray absorption and do not promote the formation of artifacts in the images are suitable as material for the positioning arrangement. The formation of the positioning arrangement as a mat composed of a closed-cell foam, for example PE foam as distributed under the name EVAZOTE 50, is preferred.
The reference member preferably has an oblong shape and the recess is disposed in the positioning element so that the longitudinal axis of the reference member proceeds substantially parallel to the longitudinal axis of the positioning element. Given human patients, a parallel attitude of the reference member relative to the spinal column is then established.
In order to make the position of the reference member visible, and thus facilitate its relative position to the region of the patient that is to be simultaneously scanned with the reference member, the seating surfacexe2x80x94in one version of the inventionxe2x80x94is provided the markings indicating the axial position of the reference member. These markings are preferably fashioned such that they do not tend to become contaminated and are easy to clean.
The positioning arrangement is preferably provided as an overlay for a positioning plate and can be provided with fasteners, for example Velcro(copyright) bands, for fastening to the positioning plate.
In an especially preferred embodiment of the invention, the positioning arrangement is displaceable in the direction of the longitudinal axis relative to the positioning plate in order to be able to adapt the position of the reference member to different patient sizes.
When the positioning arrangement is provided as an overlay for a positioning plate, in a version of the invention the positioning arrangement is provided with at least one oblong projection that overlaps a limiting edge of the positioning plate. A contamination of the positioning plate is thus largely prevented. Repositioning of the patient is facilitated when the material of the positioning means is resilient, since this avoids the patient having to be transported over a hard edge of the positioning plate.